1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to, for example, a semiconductor device, a display device, a light-emitting device, a power storage device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to, for example, a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor.
2. Description of the Related Art
Power consumption of an FPGA (LSI) can be reduced by performing logic operation at low voltage as in a general circuit. Meanwhile, a signal output through an I/O terminal is required to be at a level similar to that of voltage of an external circuit to compensate a stable circuit operation or to perform voltage matching with the external circuit. In general, with the use of a DC-DC convertor circuit such as a boosting circuit or a level shifter, an internal low-voltage signal is changed to a high-voltage signal that is output to outside.
To reduce power consumption, it is very effective to stop power supply of a high-voltage circuit. However, when power supply of the high-voltage circuit is stopped, a power source system of the high-voltage circuit needs to be controlled by a low-voltage circuit. In the case where the low-voltage circuit operates in a low-voltage region where voltage is lower than or equal to threshold voltage, the on-state current of a transistor is extremely low; as a result, it takes a long time to drive a large load. Furthermore, the high-voltage circuit directly driven by the low-voltage circuit causes a problem in that, for example, shoot-through current is generated; thus, it is difficult to control driving of the high-voltage circuit by the low-voltage circuit. In Non-Patent Document 1, a level shifter configured to convert a low-voltage signal into a high-voltage signal at high speed is described as a solution of the above problems.